Recently interest has been increasing in the development of methods for controlling motor temperature in certain appliances. For example, management of drive motor thermals has been found to be of significant importance for laundry appliance performance. Such temperature management processes are, however, difficult in the absence of a convenient method to measure motor temperature.
Previous efforts to monitor motor temperature have involved inclusion of a motor temperature sensor that is designed to “trip” to disconnect the motor from its power source upon reaching a predetermined temperature. Other processes have been developed that include injection of a direct current (DC) into the motor windings to measure motor winding resistance as it varies with temperature. This DC injection method, however, is not available in a line fed AC drive system absent addition of a DC power supply and additional control circuitry. Another challenge with using AC excitation is that the motor generally needs to be static. This is typically achieved by exciting both windings of a split phase AC motor without the normal starting capacitor in circuit thereby reducing the start torque to nearly zero.
While these techniques may be effective, there are additional disadvantages and complications in implementing such a system. Thus, a need exists for a system and method for monitoring motor temperature during an operational cycle of a laundry machine. By so doing certain disadvantages including, for example, the tripping of a motor thermal protection device with its consequent lengthy reset time further delaying completion of the laundry cycle may be avoided.